Cache the results of slow math operations on machines that don't...

src/heap.h

Index: src/heap.h
===================================================================
--- src/heap.h	(revision 2785)
+++ src/heap.h	(working copy)
@@ -28,8 +28,11 @@
 #ifndef V8_HEAP_H_
 #define V8_HEAP_H_
 
+#include <math.h>
+
 #include "zone-inl.h"
 
+
 namespace v8 {
 namespace internal {
 
@@ -1519,6 +1522,89 @@
   int previous_marked_count_;
 };
 
+
+class TranscendentalCache {
+ public:
+  enum Type {ACOS, ASIN, ATAN, COS, EXP, LOG, SIN, TAN, kNumberOfCaches};
+
+  TranscendentalCache(Type t);
+
+  static inline Object* Get(Type type, double input) {

[Søren Thygesen Gjesse, 2009/09/01 08:40:31]

Please add a (short) comment on this public Get function.

+    TranscendentalCache* cache = caches_[type];

[Søren Thygesen Gjesse, 2009/09/01 08:40:31]

The description says "Cache the results of slow math operations on machines that
don't have hardware fpu instructions to execute them.", however it looks as if
the cache is always enabled. Is that intentional?

[Erik Corry, 2009/09/01 09:02:28]

The cache only works in the runtime system.  If we have an instruction for the
transcendental then we generate it inline and never normally enter the runtime
system.

+    if (cache == NULL) {
+      caches_[type] = cache = new TranscendentalCache(type);
+    }
+    return cache->Get(input);
+  }
+
+  // The cache contains raw Object pointers.  This method disposes of
+  // them before a garbage collection.
+  static void Clear();
+
+ private:
+  inline Object* Get(double input) {
+    Converter c;
+    c.dbl = input;
+    int hash = Hash(c);
+    Element e = elements_[hash];
+    if (e.in[0] == c.integers[0] &&
+        e.in[1] == c.integers[1]) {
+      ASSERT(e.output != NULL);
+      return e.output;
+    }
+    double answer = Calculate(input);
+    Object* heap_number = Heap::AllocateHeapNumber(answer);
+    if (!heap_number->IsFailure()) {
+      elements_[hash].in[0] = c.integers[0];
+      elements_[hash].in[1] = c.integers[1];
+      elements_[hash].output = heap_number;
+    }
+    return heap_number;
+  }
+
+  inline double Calculate(double input) {
+    switch(type_) {
+      case ACOS:
+        return acos(input);
+      case ASIN:
+        return asin(input);
+      case ATAN:
+        return atan(input);
+      case COS:
+        return cos(input);
+      case EXP:
+        return exp(input);
+      case LOG:
+        return log(input);
+      case SIN:
+        return sin(input);
+      case TAN:
+        return tan(input);
+      default:
+        return 0.0;  // Never happens.
+    }
+  }
+  static const int kCacheSize = 512;
+  struct Element {
+    uint32_t in[2];
+    Object* output;
+  };
+  union Converter {
+    double dbl;
+    uint32_t integers[2];
+  };
+  inline static int Hash(const Converter& c) {
+    uint32_t hash = (c.integers[0] ^ c.integers[1]);
+    hash ^= hash >> 16;
+    hash ^= hash >> 8;
+    return (hash & (kCacheSize - 1));
+  }
+  static TranscendentalCache* caches_[kNumberOfCaches];
+  Element elements_[kCacheSize];
+  Type type_;
+};
+
+
 } }  // namespace v8::internal
 
 #endif  // V8_HEAP_H_